Water Properties and Biological Significance

Water in the Cells

• All living things consist of one or more cells with their own cytoplasm.
• Cytoplasm is the main component, containing cytosol (a gel-like substance), organelles like mitochondria, macromolecules, and ions.
• Cytosol is the liquid component of the cytoplasm surrounding intracellular organelles.
• Cytoplasm is the contents of a cell except for the nucleus, including all organelles and the cytosol.
• Cytosol is the medium for cellular metabolism, consisting of 70% to 80% water and is usually colorless.
• Cellular metabolism occurs inside the watery cell contents.
• Water is required for cellular processes like photosynthesis, where carbon dioxide and water produce glucose and oxygen.

Water Around the Cells

• A tissue is a group of cells with a similar function.
• Connective tissue contains a cellular and a non-cellular component.
• Blood is a connective tissue comprised of 45% red/white blood cells and 55% blood plasma.
• Blood plasma is approximately 92% water.

Water in Living Beings

• Water composes about 60-70% of the human body and up to 60-95% of other living things.
• Water is critical for life.
• Brain: 75% water
• Blood: 83% water
• Heart: 79% water
• Bones: 22% water
• Muscles: 75% water
• Liver: 86% water
• Kidneys: 83% water

Origin of Life in Water

• Life likely evolved in a marine (aquatic) environment.
• First came macromolecules, then organelles, and finally cells.
• Hydrothermal vents in the deep ocean provide an environment for life despite lacking light.

Water's Polarity

• Hydrogen and oxygen form covalent bonds in water molecule
• Hydrogen has a slightly positive charge (H+), and oxygen has a slightly negative charge (O-).
• Water's polarity results in water molecules attracting other water molecules and other polar molecules and ions.
• Substances that dissolve in water are hydrophilic.
• Salt consists of sodium chloride (NaCl), where the chemical formula is NaCl.
• The positive portion of water molecules (hydrogen+) attracts negative chloride ions (Cl-).
• The negative portion of water molecules (oxygen-) attracts positive sodium ions (Na+).
• Sodium chloride (NaCl) reacts with the cytosol of a cell and becomes negative chloride ions and positive.
• Ions are important in the context of cellular processes.
• A decrease of chloride ions (Cl-) in an egg's cytosol changes the electronegativity of the cytosol from negative to positive.

Properties of Water

• Three states: gas, liquid, and solid.
• High heat capacity.
• Heat of vaporization.
• Solvent properties.
• Cohesive and adhesive properties.

Water States

• In liquid water, hydrogen bonds constantly form and break as water molecules slide past each other.
• In gas water: as heat rises (as the water boils), water molecules' higher energy causes hydrogen bonds to break completely, allowing water molecules to scape to the air as gas/steam
• In solid water, when the water temperature reduces and the water freezes, the water molecules form a crystalline structure that is maintained by hydrogen bonding.
• Water's lower density in its solid form is due to the way hydrogen bonds orient as they freeze: meaning the water molecules push farther apart compared to liquid water
  • Ice floats at the surface of liquid water due to lower water density in its solid form.
• Ice crystals that form upon freezing rupture the delicate cell membrane and proteins required for living cells to function.
• Adding the solution glycerol makes it difficult for ice to form because this solution binds with the hydrogen bonds of water

Water's High Heat Capacity

• Water's high heat capacity happens because of hydrogen bonding among its molecules.
• A small amount of water can hold a lot of heat without its temperature rising.
• It takes a long time to heat water and a long time to cool it.
• Blood plasma is mostly water, which is a great way to disperse and save heat in the body.
• Induction of fever requires ATP.
• A 1°C rise in body temperature requires a 10-12.5% increase in metabolic rate.

Water's Solvent Properties

• Water is a polar molecule with slightly positive and negative charges.
• Ions and polar molecules can dissolve in it easily, making water a great solvent.
• Ions and polar molecules form hydrogen bonds with water.

Cohesive and Adhesive Properties

• Cohesion means water molecules are attracted to each other because of hydrogen bonding.
• Cohesion allows for surface tension.
• Surface tension is the capacity of a substance to withstand rupturing when placed under tension or stress.
• Water appears higher on capillary tube sides because water molecules are attracted to a capillary's charged glass walls more than to each other.
• Adhesive forces create a "pull" on the water column.
• Pull results from the tendency of water molecules evaporating on the plant's surface to stay connected with the water in the plant.

Explore water's unique properties like attraction and its role in dissolving substances. Understand how water interacts with ions in solutions, such as sodium chloride. Investigate the impact of water in biological contexts, from blood plasma composition to early life evolution.